1. Field of the Invention
The present invention relates to a picture archiving communication system for medical application (hereinafter referred to as "PACS") having a data base for archiving medical images and accompanying data.
2. Description of the Related Art
A standard PACS has a structure as shown in FIG. 1. As shown in FIG. 1, diagnosing apparatuses 100 include a CR (Computed Radiography), an X-CT (x-ray tomographic imaging apparatus), an MRI (nuclear magnetic resonance imaging apparatus), a DF (digital fluorography apparatus), a US (ultrasonic diagnosing apparatus) and an NM (nuclear medicine apparatus). Image data collected by the various diagnosing apparatuses 100 is registered in a data base 300 via a network 200. On the other hand, when image data is referred to by work stations 400 (WS) arranged at various locations, a desired image index (ID) (e.g. a number assigned to each image) or an examination index is delivered from the work station 400 to the data base 300 to request transfer of image data. In response to a command from a system manager 500, image data corresponding to the work station 400 (WS) is transferred and displayed on an image display such as a CRT.
The data base 300 of the PACS, as shown in FIG. 2, comprises a optical disc library 310 having an optical disc drive 312, a magnetic disc drive 320, a system control unit 350, and a network interface 340. These devices are connected to a data bus 330. In this case, the system control 350 comprises a CPU 352 including a memory, an optical disc file management unit 354, and a magnetic disc file management unit 356.
In the data base system having the above structure, image data is normally stored in an optical disc drive 312. If the optical disc library 310 including a plurality of optical disc drives 312 is used, a large quantity of image data can be stored. In this case, however, the access time increases to several-ten seconds. If image data is stored in the magnetic disc drive 320, the access time of image data can be decreased. However, the storage capacity of the magnetic disc drive 320 is lower than the optical disc drive 312.
In general, among image data stored in the optical disc drive 312, image data likely to be accessed in the future (within a few days) is estimated, and such data is copied from the optical disc 312 to the magnetic disc drive 320 in advance. This processing is called "migration processing".
FIG. 3 is a view for explaining the overall operation of the PACS in the "migration processing" mode. Referring to FIG. 3, the system manager 500 supplies at least one image index ("image ID" hereinafter) to the data base 300. The image ID is supplied to the CPU 352 of the system control unit 350 in the database 300 shown in FIG. 2. Then, the system control unit 350 accesses the optical disc file management unit 354 and finds the physical address for the optical disc drive 312, thereby reading out the corresponding image data. Subsequently, the system control unit 350 accesses the magnetic disc file management unit 356 and finds the address to be written, thereby writing image data read out from the optical disc drive 312 at the corresponding address of the magnetic disc drive 320.
FIG. 4 is a flow chart showing the migration processing in detail.
When a program is activated by a migration command from the system manager 500, each image ID is read out one by one from the memory provided within the CPU 352 (step ST1).
Then, the optical disc file management unit 354 is accessed, and the physical address associated with the image ID of the optical disc drive 312 is found (step ST2). In step ST3, it is determined whether the image data corresponding to the image ID is present at the address of the optical disc drive 312. If "NO" in step ST3, the arm of the optical disc library 310 is actuated, and a desired optical disc drive 312 is mounted (step ST4). If "YES" in step ST3, or after step ST4, desired image data is read out from the optical disc drive 312 (step ST5) and the control routine goes to step ST6. In step ST6, the magnetic disc file management unit 356 is accessed, and the address for write of desired image data is found. The image data corresponding to the image ID is written at the corresponding address of the magnetic disc drive 320 (step ST7).
Referring to the flow chart of FIG. 4, the processing of one image ID was described. After the steps ST1 to ST7 are completed, the control routine goes back to step ST1, and the same processing is repeated. Once the migration processing for all desired image IDs have been completed, the completion is told to the system manager 500 (step ST8) and the entire processing is finished.
After the end notice of the migration processing is transmitted to the system manager 500, the system manager 500 supplies a command to the work station 400, as shown in FIG. 3, to read out all image IDs which have been subjected to the migration processing. Thereafter, a command for reading the image ID is supplied from the work station 400 to the data base 300. Thus, desired image data is transferred from the magnetic disc drive 320 to the work station 400.
In the PACS with the above data base 300, the capacity of the magnetic disc drive 320 is limited. Thus, it is necessary to delete unnecessary files on an as-needed basis. In this case, the magnetic disc drive 320 stores, in a mixed manner, modalities, data registered by the work station, etc., data read out from the optical disc drive 312 in the migration processing, data used temporarily as buffer, and data for backup of data on the system disc and memory, etc. Accordingly, when data in the magnetic disc drive 320 is deleted, such data is generally deleted by referring to the earliest date of access of files.
However, when data transfer is performed in the data base 300 after a certain period from the migration processing, it is possible that part of a desired file is deleted before the data transfer. The fact of deletion of data is not detected in the system manager 500 or work station 400. Consequently, when data is accessed by the work station 400, desired image data is not in the magnetic disc drive 320 and the optical disc drive 312 must be accessed once again. Thus, the wait time increases considerably.